Brendan Rodgers' side were made to work by Rangers during a thrilling opening 45 minutes at the Ibrox on Saturday.
Goals from Tom Rogic and Leigh Griffiths after the break wrapped up a 2-0 win for the Scottish champions, which increased their incredible domestic unbeaten run to over 500 days.
However, Swedish defender Lustig concedes that the result could have been very different were it not for Gordon's crucial intervention.
The Scotland No 1 made an instinctive save to stop Alfredo Morelos levelling for the home side with a header from point-blank range just moments after Rogic broke the deadlock.
Right-back Lustig told CelticTV: "Maybe Rangers had a short two or three minute spell just after we scored but after that we were really comfortable.
"Craig made a top-drawer save to keep it at 1-0. You need a really good keeper in these games and we have got that in Craig.
"His save was vital. Maybe had they gone to 1-1 it could have been a different game.
"But from that moment one we proved we're the best team again."
Brendan Rodgers has won six of the seven clashes against the Gers since taking over at Hampden Park last year, and this latest victory was the perfect warm-up for Celtic as they prepare for the Champions League clash with Anderlecht on Wednesday night.
Lustig hopes they can build on the Old Firm Derby triumph and pick up a win which would put them in good stead for a Europa League slot.
He said: "We know it's a massive game on Wednesday, especially as we were not satisfied with the game against PSG.
"We want to be in Europe [after New Year] so hopefully we can grab some points and play some good football."